1. Field of the Invention
The present invention relates to exposure devices used in lithographic processes for the manufacture of liquid crystal displays, integrated circuits, thin film magnetic heads, etc., and to stage and corresponding position detection devices suitable for use with such exposure devices.
2. Description of the Related Art
Lithographic processes utilized during the manufacture of liquid crystal displays, integrated circuits, and other similar devices usually involve exposure devices. Such exposure devices have been used to image a mask pattern onto a substrate. Such exposure devices include step and repeat type devices (often referred to as a xe2x80x9cliquid crystal stepperxe2x80x9d) and batch transfer scanning type devices which transfer a pattern of a mask onto a plate (e.g., a glass substrate). Such devices typically scan a mask stage and a plate stage in the same relative direction with respect to a projection optical system.
Recent developments have been made in regard to exposure devices as a result of increased demand for larger liquid crystal displays, etc. Accompanying such increases, plate sizes within exposure devices have correspondingly increased. Accordingly, scan type exposure devices have been developed which are capable, of exposing a large surface compared to a stepper, and which perform exposures of plural shots with respect to one plate.
Exemplary exposure devices are illustrated in several drawing figures which have been attached to this patent document. Reference is now made to drawing figures identified as FIGS. 5, 6, 7, and 9, respectively.
FIG. 5 shows a batch transfer type scanning exposure device. FIG. 6 shows in more detail the stage control device 101 shown in FIG. 5. In FIG. 5, a mask stage MST and plate stage PST are respectively supported on air pads (not shown in the drawing) on an upper surface plate 102a and a lower surface plate 102b which make up the body column 102 which supports the projection optical system PL. The mask stage MSK and plate stage PST are moved by linear motors 104 and, 106 in right and left scanning directions. The stator 104a of the linear motor 104 which drives the mask stage MST is fixed to the upper surface plate 102a, and its moving element 104b is fixed to the mask stage MST. Moreover, the position of the mask stage MST in the scanning direction is constantly measured by means of a laser interferometer 108 which is fixed to the body column 102.
The stator 106a of the linear motor 106 which drives the plate stage PST is fixed to the lower surface plate 102b, and its moving element 106b is fixed to the plate stage PST. The plate stage PST is equipped with a moving table 110 to which moving element 106b is fixed, and with a substrate table 116 which is loaded on this moving table 110 via a Zxc2x7xcex8 movement mechanism 114. The position of the substrate table 116 in the scan direction is constantly measured by means of a laser interferometer 112 which is fixed to the body column 102.
The arrangement of stage control device 101 is now described with reference to FIG. 6. As shown in FIG. 6, a position control loop of the plate stage PST includes interferometer 112, a subtractor 118, a plate stage servo operating unit 120, a plate stage drive amplifier 122, and linear motor 106 which is driven by the drive signal S2 output from plate stage drive amplifier 122. Moreover, plate stage position information S1 from the interferometer 112 is fed back as input to the plate stage servo operating unit 120 via a differencing unit 124. Accordingly, a speed control loop is constituted as the inner loop (minor loop) of the position control loop. The reference position is input from the reference value output unit 126 with respect to the subtractor 118 of the aforementioned position control loop. By means of the position and speed control loop of the plate stage PST constituted in this way, position and speed control of the plate stage are performed such that the position deviation, which is the difference of the reference position and the output of the interferometer 112, becomes zero.
Similarly, a position control loop of the mask stage MST includes interferometer 108, a subtractor 128, a mask stage servo operating unit 130, a mask stage drive amplifier 132, and the linear motor 104 which is driven by the drive signal S4 output from mask stage drive amplifier 132. The plate stage position information S1, which is the output of the interferometer 112 with respect to the subtractor 128 of this position control loop, is input as the reference position. Accordingly, by means of the position control loop of the mask stage MST, slave control of the mask stage MST is performed with respect to the plate stage PST, such that the positional deviation, which is the difference of the output S1 of the interferometer 112 and the output S3 of the interferometer 108, becomes zero.
Referring now to FIG. 9, depicted therein is another scanning type exposure device. In particular, an illuminating optical system 201 and a projection optical system 204 are fixed to a base 210 by means of a B column 208. On a carriage 207 for scanning use arranged to move freely with respect to base 210 there is located a mask 202 which is movable a small amount with respect to carriage 207 via a mask stage 203. A substrate 205 is located such that a substrate stage 206 is movable a small amount with respect to the same carriage 207 (the fixed portions are drawn with thick lines, and the movable portions with thin lines). By scanning the carriage 207, the mask 202 and substrate 205 scan in a predetermined direction with respect to the projection optical system 204, and the pattern of the mask 202 successively transfers onto the substrate 205. A laser interferometer 222 is supported by an A column 209, and by means of the interference of light reflected from a fixed mirror 211 arranged in the projection optical system 204 and light reflected from a moving mirror 212 arranged in the substrate stage 206, the position of the substrate stage 206 with respect to the projection optical system 204 is detected. The position information of the substrate stage 206 from the laser interferometer 222 is input into the main control device 240. The main control device 240 is equipped with a speed adjustment operating unit 218 which outputs speed adjustment instructions according to an exposure program. A servo operating unit 220 calculates and outputs the drive signals for the carriage 207 based on the difference of the speed adjustment instructions and the position information of the substrate stage 206, and for a drive amplifier 221 which amplifies the output of the servo operating unit 220. The control unit 217 controls the carriage 207 by means of the output of the drive amplifier 221. The laser interferometer 222, main control device 240 and control unit 217 make up a servo loop that controls the carriage 207. That is, the substrate stage 206 is positioned based on the position information of the substrate stage 206 and the speed adjustment instructions output from the speed adjustment operating unit 218.
Despite their widespread use, the exposure devices discussed above are not without their problems. For example, in a closed loop control system, the bandwidth or the frequency at which the gain of the closed loop frequency characteristic becomes (xc2xd)-fold of the low frequency gain as the frequency xcfx89xe2x86x920, and when expressed in dB, falls 3 dB from the low frequency gain of xcfx89xe2x86x920.
With a stage control system as shown in FIG. 6, the plate stage control performance is set, for example, by means of the response band of the plate stage position and speed control loop during the fixed speed control (uniform speed control) of the plate stage performed in the scanning exposure time, the variable speed, adjustment characteristics, speed fluctuation, or during the position setting control of the plate stage performed in the shot interval stepping times in the case of step and scan type of exposure device, the variable speed, speed adjustment, position setting accuracy and the like.
Nevertheless, in the aforementioned prior art stage control device, measuring the position of the substrate table 116 by means of the interferometer 112, separated from the linear motor 106 which is the drive source, based on this the substrate table 116 and the moving element 106b of the linear motor 106, with respect to the moving table 110 which was fixed, position control of the scanning direction of the plate stage to the unrelated Zxc2x7xcex8 movement mechanism 114 exists. Low frequency mechanical natural vibrations as a resonant mode are included in the plate stage position and velocity control loop. In this case, for example, during drive of the plate stage, when the resonant frequency rises beyond the aforementioned Zxc2x7xcex8 drive mechanism 114, because the position information of the substrate table 116 which received the effects of this resonant frequency is input as feedback into the position control loop, it becomes difficult to control the position and speed of the plate stage. Accordingly, in prior art stages control systems, the response band of the position and speed control loop of the plate stage cannot be made sufficiently wide, and as a result, there is the disadvantage that the plate stage control performance cannot be made sufficiently high.
In FIGS. 7(A) and (B), the frequency response characteristics and phase characteristics of the position control loop of the plate stage PST are respectively shown, in the prior art stage control system when the frequency of the aforementioned resonant vibration was 60 Hz. As is clear from FIG. 7, the response band of the plate stage became about 10 Hz.
Moreover, as a result that the plate stage control performance can not be made sufficiently high, overshoot arises after the end of variable speed of the plate stage PST (response of the system exceeding the expected value in the case that a sudden change occurred in the input, or overshooting amount), undershoot (the reverse of overshoot; the response does not reach the expected value, in the case of a sudden change in the input) becomes large, and is an inconvenience that the mask stage slave control performance becomes poor, while performing the plate stage position as a position instruction.
However, a problem similar to the aforementioned plate stage movement problem arises in an XY stage of a 2-stage structure which loads the X stage via a drive mechanism of the X stage on the upper portion of the Y stage, or in the fine movement stage loaded via the upward drive mechanism of the coarse movement stage in the control system of a reticle stage of the so-called coarse-fine movement structure.
Furthermore, in the scanning type exposure device of FIG. 9, effects are realized as a result of the vibration of the movement of the carriage 207 or of other devices, and because the B column 208 vibrates at its natural vibration frequency, for example 50 HZ. In order to avoid oscillation, the control band of the aforementioned servo loop can only be taken as at most ⅓ of this, around 10 Hz. Accordingly, this becomes a bottleneck, and the control performance of the servo loop cannot be raised.
The present invention""s principle objects are to solve the problems mentioned above and to provide a stage control device for use with an exposure device that delivers increased stage control performance. The present invention provides for increased control performance of a stage without realizing the effects of vibration often associated with stage position detection. By providing such a stage control device, the present invention delivers increased throughput and pattern transfer accuracy.
Accordingly, the present invention provides an exposure device that includes a stage device having a first stage which movably supports an object and a drive mechanism which drives the first stage in at least a first direction. The first stage has a first portion for supporting the object and a second portion coupled to the drive mechanism. The first stage device is configured with a first position detecotor which optically measures the position of the first portion in a predetermined measurement direction. The exposure device further includes a second position detector which optically measures the position of the second portion in the same predetermined measurement direction.